First Peak Fractal Analysis of Optical Coherence Tomography Angiography in Eyes with Papilledema

Abstract

Purpose : To evaluate fractal analysis box size resolution and self-similarity breakdown in the box counting method of fractal analysis in eyes with papilledema and controls imaged with optical coherence tomography angiography (OCTA)

Methods : A retrospective study was performed using 49 eyes with papilledema and 40 control eyes. OCTA images consisted of 4.5x4.5mm peripapillary scans obtained with the RTVue XR Avanti (Optovue Inc., Fremont, CA), standardized and binarized using ImageJ (NIH, Bethesda, MD). Fractal dimension (FD) was determed by means of a box-counting algorithm which used box sizes with increasing exponential factor of two with grid algorithm using Fractalyse (ThéMA, Besançon Cedex, France). FD was plotted against linear box dimension and first maximum (first peak) that represents the smallest box size resolution before breakdown of self-similarity. Statistical analysis was performed using one-way analysis of variance with post-hoc Tukey HSD. Further analyses were performed on papilledema subgroups, which were based on severity (Grade 0, n=12; Grade 1, n=15; Grade 2, n=13; Grade 3, n=5; Grade 4/5, n=4).

Results : There was no significant difference in the mean box size in the papilledema group compared to the control group (8.0 ± 0.0). There were also no significant differences in box size for first peak in each of the papilledema subgroups from Grade 0 to Grade 4/5.

Conclusions : The first peak box size of fractal dimension, as a function of decreasing box size, represents the smallest box size resolution prior to loss of uniformity of the vascular pattern’s fractal dimension. We previously reported that the first peak occurs at larger box sizes in diabetic retinopathy and primary open angle glaucoma compared to controls, indicating the loss of the vascular patterns' self similarity at smaller resolutions and loss of microvasculature. In this study, the first peak box size was not significantly different between eyes with papilledema and control eyes, indicating no significant loss of fractal self-similarity, or loss of peripapillary microvasculature in papilledema, regardless of severity. Fractal analysis in OCTA appears to reveal some useful quantitative insight into the peripapillary microvascular pathology of papilledema.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.